What to do if I’m expecting and want to give up my parental rights so that my baby can be raised by his father and his wife?

You need to get a family law attorney involved and work out an agreement with the father of the child.  You can voluntarily give up your child, but it would also require his consent-- because he would technically have the right to ask for child support from you for him having to raise the child.

Once you have everyone on board, the family law attorney can help you sign an affidavit to relinquish your rights.  The attorney would need to file a petition to have you legally declared mom, and then to terminate your rights.  In the same suit, he would legally be declared "dad."  If his wife wants to adopt the child, the termination suit can (and usually is) combined with a petition for her to adopt the child.  Neither the petition nor the affidavit can be filed until the child is born-- but keep in mind, this is not a quick process and can take up to six months or more to complete... so the more preplanning that you do the better.  Once the child is born, then everything can be ready to proceed forward without any delays. 

Adoptions can be tricky if the waivers and petitions are not done properly-- that's why you want to have a family law attorney help both of you.  "Dad" can hire the attorney and they can prepare any of the required affidavits.  If neither of you can afford an attorney, call around to a few churches.  There are a few programs under the 'pro-life' movement that offer adoption assistance to unwed mothers.  They may be able to help, especially if everything is agreed to.